Noiseless recording



Patented Oct. 19, 1937 UNITED STATES T OFFICE NOISELESS RECORDING Application October 30, 1934, Serial No. 750,628

9 Claims.

The invention relates to noisless recording and has for an object to record sound waves on film in such a manner that the positive print will have substantially high opacity in the sound track where the sound record is of low level or does not appear. This reduces .ground noise due to the film, when using a positive print to reproduce the sound. v

In anti-ground noise devices it has been'common to energize the noise reduction circuit through a bridging amplifier and it may readily happen that faulty operation of the noise reduction circuit is caused by faultyoperation of the intervening elements in the noise reduction circuit between the bridging bus and the film itself.

An object of the invention is to largely remove the possibility of such faulty operation. This is accomplished by controlling the noise reduction in response to the modulated light to be recorded, whereby this modulated light is the motivating influence for noise reduction control. It

.is of advantage to furnish a noise reduction element which is controlled by'the light passing to the film and which responds to, the quality of the modulated light rather than responding to the quality of the electrical energy appearing in the bridging bus.

The invention may be applied to an arrange- ,m'ent wherein the refinements heretofore proposed, and according to which the bias on a light valve is actuated by the envelope of the sound currents, or according to which the envelope of a variable area sound record is closely and accurately' followed by a shuttering device, are not necessary, and in fact may have the following disadprovement, according to which, method and means responsive to the modulated light are provided for restricting the recording light in the same sense'as the recording at a fixed small amount sufficient to permit low level sounds to be recorded without substantial distortion, and at all higher level sounds for removing said restricting effect from influencing the recording.

The above reference, and the similar reference in the claims, to restricting the recording light in the .same sense as the recording, is to be understood as meaning that for a variable area record the tiontherefore being in opposite senses, in order to record the volume in modified form. V On the other hand, the invention may be applied to known arrangements wherein the noise reduction control is proportional to the intensity of the light beam to be recorded.

For further details of the invention, reference may be made to the drawing wherein:

Fig. 1 is a diagrammatic illustration of a negative variable area sound track according to the present invention as applied to still control of noise reduction.

Fig. 2 is a diagrammatic circuit and optical arrangement for recording the sound track of Fig. 1. Fig. 3 is a view illustrating in further detail the optical elements of Fig. 2. I

Fig. 4 is a diagrammatic illustration of a negative variable area sound track resulting from the .25 modified recording circuit of Figs. 5 and 6, and showing shuttering proportional to the amplitude of the recorded light waves.

Figs. 5 and 6 illustrate two different modifications of Fig. 2 for recording the type of sound block of Fig. 2, with its mirror in modified position.

Fig. 8 is a detailed View partly in section, of the shutter mechanism of Figs. 2 and 3.

Referring to the drawing, the negative film I in Fig. 1 has a sound track width represented by the dimension 2. I provide alight beam controlled shutter, to be described later, this shutter being arranged so that for low level sounds, e. g. from 0- of the total track width, the sound track is shuttered a fixed amount represented by dimension 3. For all modulations requiring more than this fixed amount of track area, the shutter is entirely removed, and this is accomplished gradually 4,5 as illustrated by the curved portion 4 of the shuttered area. It will be noted that there is a time lag between the appearance of high level peaks illustrated by 5 and 6, and the point illustrated at 1 where the shutter is entirely removed. Also, 15 when the sound reaches a low level, e. g. a level which can be recorded within of the track width, the shuttering efiect. again comes into play asillustrated at 8. Again there is a time lag between the disappearance of the high level peak as illustrated at 9,1andthe'full effectiveness of i the shutter as illustrated at point 10. H

"the lamp l1 and the'mirror I6 is arranged a mask 1 18 having a' D-shaped opening'as shown. 7 Light 1 from theimirror J6 isrefiected to a slit bloc'k 19,

the light passing therethrough impinging partly on shutter as shown at 2'], enough of the light passing .through the slit block [9 passing by the' front edge of shutter 20 to accommodate the low level excursions of the mirror l6, as'explainedin connection with Fig: 1. The light which passes by 1 the shutter 20 is focused by a' suitable lens system I22 onto thenegativefilm l2. g

A mirror is mounted on slitblo ck I!) in a position; and so tilted that it receives light from mirror 1-6 for all 'excursions'thereof greater than are recordable with the amount of shuttering shown at 3 in Fig. 1, and reflects such light to a of light and; the removal of course persists. for' all the lenses '22, an image of light sensitive device such as a caesium or selenicell 34 to remove shutter 20 as illustratedat'l in Fig. 1. The removal of shutter 20 is effected as soon as mirror 25 receives any appreciable amount greater amounts of light" The celli34 operates shutter 20 through an obvious circuitincluding -potentiometer 35, amplifier'36, rectifier 3T, relay '38, battery'39, contacts 40, potentiometer 4|;and

coil 29.} When mirror 25 no longer receives light from mirror 16; the relay 3 8 and shutter 20 assume the positions shown in Fig. 2. I r

Further details of the optical system of Fig. 2 areillustrated in Fig. 3, wherein lenses 23 and 2 4 are arranged at opposite sides of the mask I8, a. lens '26 being provided. adjacent mirror I6, and lens 21 beingjarranged in front of the slit block I9 which carries mirror 25 for cell 34. The optical arrangement is such thatthe image of "the filament of lamp I1 is focused at mirrorl6 and at the mask l8 appearing onthefilml2. The shutter 20, as shown in Fig. 8, may be mounted on a reed '28 which carries 'an actuating coil 29 arranged in the air gap 30 of a field magnet 3|; The terminalsof the coil'29 may be brought j 7 r 'to binding posts 32 and 33. Stops. 42 and 43 may t p .beemployed to limit the movement of shutter 20 in either direction. 1 They stops 42 and 43 may be omitted, the two positionsof shutter 20 being determined by the initial positionof shutter 2llwlien f relay 38 isopen; and bythe. throw of shutter 20 when the relay 38 is closed. *The'r'ange of movement of shutter 20 may be controlled by potentiometer, or sensitivity control 4l.1 A positive print of the negative film in Figs. 1 and 4 willof course j havetransparent and opaque portions-in oppo- 65 site senses from that shown.

Instead of the fstep controlas in Fig. 2, the

"proportionality control of Figs. 5 and 6 maybe "employed to produce the record of Fig. 4-wherein the. shuttering 44 is proportional to the peaks of variable area record 45. For this purpose I dis: pense with relay 38, and employ rectifier '31 to supply" rectified audioimpulses to coil 29 as i'n Fig. 5, or amplifier 36 may'supply rawA; C. (audio) to'coil'29 which is now provided with a soft iron "magnet 46. 'Also as shown in Fig. 7, the mirror 25 is arranged with its edge substantially coinciding with the "straight edge of the D-shaped spot of "light reflected from galvanometer l5 when the latter is ole-energized, whereby mirror 25 receives an amount oflight proportional at all times to the excursions of mirror. 16.. Y e I f V The invention is also applicable to variable density recording.

Having thus described the invention; what is claimed asnew and desired to secure by Letters Patent, is:

I claim:

ing light :sensitive surface comprising a light source, means for modulating light from said source in accordance with the amplitudeof said sound waves, means whereby said modulated light is adapted to expose said-surface in substantially 'direct accordance with saidlight modulations and,

means .respo nsive to said modulatedlight for controlling'the exposure of said surface, said last mentioned means being positioned between said surface and said light modulating "means. a i

1. Apparatus for recordingsound' onea mov 2.. Apparatus for recording sound on a moving light sensitive surface comprising a light source,

means for modulating light from said source'in" accordance with the amplitude of said sound e V Waves, means whereby said modulated light is. adapted to 'expose' said surface in substantially direct accordance with said'ilight modulations,

and means responsive-to said'modulated light for' controlling the exposure of a portion of'said' surface Where the sound record does not appear,

means. p

-said last mentioned means'being positioned be-1 tween said' surface and said light modulating 3. Apparatus for recording; sound on'a'movingf light sensitive surface comprising a light source; means for modulating light from said source in accordance with the amplitude of said sound waves, means whereby one portion of said modusaid surface in accordance'with the envelope of said light modulations, said last mentioned means being positioned'between said surface, and said lightinodulatin'g means. a

.4. Variable area sound comprising a light source, a galvanometer therea for, an audio circuit for saidgalvanometen'a,

-shutter in'thepath of light reflected from said igalvanometer, and means positionedbetween said galvanometer and said' shutter and in the path or light reflected from 1 said galvanometer for controlling said shutter. 1 I

.40. lated light is adapted to expose said surfacein direct accordance with said light modulations, and means responsive-to anotherportion ofsaid -modulate d light for controlling'the exposure of u recording apparatus? .7 7

5. Variable area sound recording apparatus,

comp'r'ising alight source, a galvanometer there for; an audio circuit for said galvanometer, a shutter in thebpath of lightreflected from said galvanometen; and means positioned between said galvanometer andsaidshutteran'd in the 7 path of. light reflected from said galvanometer V for controlling .said shutter; said controlling means comprising means whereby said shutter is; 'effective for all vibrations'of the mirror of said galvanometer within a certain'angle, and whereof said mirror beyond .said certainangle,

Sound film recording apparatus comprising the combination of a galva'riometerfor exposing variable area on a moving film in accordance with V sound waves; means comprising a shutter asso- 1 r fciated with said galvanomet'er for preventing exposure of. the high "level portion of the; sound by said shutter is not effective for all vibrations track by a fixed amount which is sufficient to permit low level sounds to be recorded, and means positioned between said galvanometer and said shutter and associated with said shutter and responsive to wide angle deflections of said galvanometer corresponding to sound having a level higher than said fixed amount for removing the influence of said shutter on the recording.

'7. Sound film recording apparatus comprising the combination of a source of audio frequency current, a galvanometer, a light source, a mask between said light source and said galvanometer, a slit block in the path of light reflected from said galvanometer, a mirror on said slit block, a

" shutter associated with said slit block, said shutter being normally in a position to permit low level sounds to be recorded while shuttering a fixed amount, and means responsive to sound levels higher than said fixed amount, said means being actuated by reflected illumination from said mirror and thereby reduce the shuttering to a lesser fixed amount.

8. Sound filin recording apparatus for recording variable area of a film in accordance with modulated light, comprising a constant light source, means for modulating a light beam from said source, a shutter in the path of said beam, a control circuit for said shutter for moving said shutter into two positions, in one of which the high level portion of the sound track is shuttered a fixed amount to permit low level sounds to be recorded, and in the other of which said shutter is not effective, and means positioned between said shutter and said modulating means and in the path of the modulated light for actuating said control circuit.

9. Sound film recording apparatus comprising the combination of a source of audio frequency current, a galvanometer, a light source, a mask between said light source andsaid galvanometer, a slit block in the path of light reflected from said galvanometer, a mirror adjacent said slit block and in the path of wide angle deflections of said galvanometer, a shutter associated with said slit block, said shutter being normally in a position to permit narrow angle deflections of. the mirror to be recorded while shuttering a fixed amount, and means responsive to light received by said mirror for controlling said shutter.

WILLIAM E. BEATTY. 

